Preform for producing containers with an inner partition from a thermoplastic material

ABSTRACT

A preform ( 9 ) made of thermoplastic material and including a body ( 11 ) provided with an at least partially longitudinally extending inner partition ( 10 ). The preform is used for molding and particularly blow molding or stretch-blow molding a container with a body having opposed portions defining hollow recesses with inwardly-directed convex surfaces, said portions being spaced apart by said inner partition. In a straight cross-sectional view, the body ( 11 ) has a non-circular outline with two opposed portions (a, b) separated by a minimum distance (d 1 ) that is smaller than the distances between the other pairs of opposed portions of said outline. The inner partition ( 10 ) extends between said two opposed portions (a, b), and said distance (d 1 ) is such that, relative to the periphery of the body ( 11 ) of the preform, during molding, the inner partition ( 10 ) is transversely stretched at a rate equal to that at which the body ( 11 ) is transversely or peripherally stretched.

FIELD OF THE INVENTION

The present invention relates to improvements made to preforms made ofthermoplastic, having a body provided with an at least partiallylongitudinally extended internal partition and intended for themanufacture, by molding, especially by blow molding or by stretch-blowmolding, of a container whose body has opposed portions forming hollowrecesses with inwardly directed convex surfaces, said recesses beingbraced by said internal partition.

BACKGROUND OF THE INVENTION

It is known to provide containers, especially bottles, made of athermoplastic such as polyethylene terephthalate PET, polyethylenenaphthalate PEN, or another thermoplastic, with an internal partition.Such a partition may be complete, i.e. it may extend over the entireheight of the container, in order to divide the internal volume of thecontainer into two chambers containing two respective liquids which mustnot be mixed together before being poured. As shown in FIG. 1 of theappended drawing, the partition 1 may also be partial, i.e. it mayextend only over part of the length of the body 2 of the container 3, inorder to retain (bracing) two opposed portions of the body of thecontainer, for example in order to maintain two gripping recesses 4hollowed out in the body of a container filled with a pressurizedliquid, which recesses, even if they were not reinforced, would riskbeing deformed due to the effect of the pressure of the liquid.

It is known to manufacture such containers from preforms whichthemselves are provided with a totally or partially longitudinallyextended internal partition depending on the type of final container tobe obtained. Such a preform 5 with a partially longitudinally extendedinternal partition 6, intended for the manufacture of the container inFIG. 1, is illustrated in FIGS. 2 and 3 of the appended drawing,respectively as a side view in FIG. 2 and, in the case of FIG. 3, in across-sectional top view on the line II—II of FIG. 2. It has a generalstructure similar to that of a partitionless preform with a neck 7 and athick-walled body 8 which are conventionally shaped. The internalpartition 6 has a thickness appreciably smaller than that of the thickwall of the body.

When this known preform, after it has been heated, is subjected to astretching or stretch-blowing process in order to obtain a container,the internal partition stretches, as does the wall of the body: thelongitudinal stretch ratio of the partition is identical to thatundergone by the body (for example, in order to be specific, typically2.22 to 3.5 for the PET grades currently used on an industrial scale).On the other hand, when the body of the container to be obtained has tohave a localized transverse necking—for example distance between thebottom of the gripping recesses 4 of the container of FIG. 1—, thetransverse stretch ratio of the partition is locally very much less thanthe transverse (or perimetric) stretch ratio of the body of thecontainer: in order to be specific, the transverse or perimetric stretchratio of the body is generally at least about 4, while the transversestretch ratio undergone by the partition remains here less than 4.

As a result, there is a disadvantageous difference between theproperties of the material of the partition and of the material of thebody of the container: since its material has not undergone sufficienttransverse elongation, in order to orient the molecular chains in acomplementary fashion the partition is subject to deformation when thecontainer is subsequently exposed to severe conditions of use and thepartition is no longer capable of effectively ensuring its bracingfunction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a container having a partition formed therein formaintaining gripping recesses.

FIG. 2 is a drawing of a preform for the container of FIG. 1 with apartial section view of the longitudinally extended internal partition.

FIG. 3 is a cross-sectional view of the preform shown in FIG. 2 alongthe line III-III.

FIGS. 4 and 5 are cross-sectional views of preforms in accordance withthe present invention.

FIGS. 6 and 7 are cross-sectional views of preforms in accordance withthe present invention having their respective partitions joined byrounded parts of relatively large radius.

DETAILED DESCRIPTION OF THE INVENTION

The object of the invention is specifically to remedy this drawback andto provide a technical solution which allows, during the blowing orstretch-blowing process, a transverse elongation ratio substantiallyidentical for the body of the preform and for the internal partition sothat the constituent materials of each of them have appreciably similarphysical and mechanical properties and behave in a homogeneous fashion.

To these ends, and with reference to FIGS. 4 and 5 of the appendeddrawing illustrating, respectively, in a cross-sectional top view and onan appreciably greater scale than that in FIG. 3, two possibleembodiments of a preform according to the invention which are given byway of non-limiting examples, a preform 9 as indicated in the preambleis essentially characterized, being designed in accordance with theinvention, in that its body 11 has, in cross section, a noncircularoutline with two opposed portions a and b separated from each other by aminimum distance d₁ which is less than the distances separating theother pairwise opposed portions of said outline, in that the internalpartition 10 extends between said two opposed portions a, b separated bya minimum distance d₁ and in that said minimum distance d₁ is chosen,with respect to the perimeter of the body 11 of the preform, such that,during molding, the internal partition 10 undergoes a transverse stretchratio which has approximately the same value as the transverse (orperimetric) stretch ratio undergone by the body.

Moreover, because of the fact that the correct execution of theblow-molding or stretch-blow molding process virtually excludes the useof preforms having a body of geometrically too complex shape, a preform9 will advantageously be used whose body 11 has a maximum transversedimension d₃, regarded as being parallel to the internal partition 10,which is appreciably less than its maximum transverse dimension d₂,regarded as being approximately perpendicular to the internal partition10, the ratio of said transverse dimensions d₃ and d₂ then being suchthat, during molding, the internal partition 10 undergoes a transversestretch ratio which is approximately identical to the transverse stretchratio undergone by the body.

Although other arrangements may in principle be envisaged, it is,however, simpler and, for most practical applications, sufficient forthe partition 10 to extend centrally in a plane of symmetry of the body11.

It is desirable for the use of preforms according to the invention toinvolve only minimal adaptations of plants for manufacturing containersin order to obtain final containers of given shapes and properties(dimensions, thickness of the walls, thermal resistance, etc.). However,the various ways of implementing the manufacturing process and saidproperties of the final containers are dependent on the properties ofthe starting preform, and in particular on the geometrical dimensions ofits body (perimeter, wall thickness, etc.). Thus, a minimal modificationof the manufacturing conditions and of the manufacturing plants in orderto achieve a given container means that the preform according to theinvention preserves the fundamental properties of the prior preforms forthe use of which the current manufacturing plants are designed. The sameapplies in particular to the perimeter of the body.

It is therefore desirable in practice, whatever the geometrical shapegiven to the body of the preform, for the perimeter of the cross sectionof said body 11, at least in that part of the latter which is providedwith an internal partition, to maintain a value approximately similar tothat of the perimeter of the cylindrical body of revolution 8 of theconventional preform, while the internal partition 10 is, in accordancewith the abovementioned arrangements of the invention, narrower than thepartition 6 of the prior preforms.

Having established this, the body 11 of the preform 9 designed accordingto the invention may be given any shape complying with this basiccondition. In particular, the body may be cylindrical, especially with across section of oval or elliptical shape, as shown in FIG. 4; the twoaforementioned portions a and b are then the parts of largest radius ofcurvature and the internal partition 10 extends along the minor axis ofthe oval or of the ellipse, the aforementioned distances d₁ and d₃ thenbeing identical. It is also possible to provide, as shown in FIG. 5, abody having a bilobate outline, the partition 10 extending between thetwo lobes 12; here, the aforementioned portions a and b are angularparts joining the two lobes together.

In order to facilitate the stretching process and to reinforce thecontainer, it is desirable for the partition 10 to be joined to the wallof the preform by rounded parts of relatively large radius, as shown inFIGS. 6 and 7 which correspond respectively to FIGS. 4 and 5.

In the same way as for the prior preforms, the internal partition mayhave a total or partial longitudinal extent with respect to the body ofthe preform. In the case of a partial partition, provision mayoptionally be made for the particular shape given to the body 11 of thepreform according to the invention to extend longitudinally only incorrespondence with the partition and, in the case of the rest of itslongitudinal extent, for the body to be a cylinder of revolution, as inthe case of a conventional preform.

By virtue of the arrangements adopted in accordance with the invention,an improved preform is produced which is capable of leading to a finalcontainer having an internal partition which has uniform properties andwhich is capable of withstanding, during use, thermal and/or mechanicalstresses without thereby resulting in appreciable deformation of theoverall body, including deformation of the portions of the latter whichpreviously were subject to being deformed due to the effect of thepressure of a pressurized filling liquid and which are now correctlyretained by the correctly stretched partition which appropriatelyfulfills its bracing function.

As goes without saying and as has already resulted from the foregoing,the invention is in no way limited to those of its modes of applicationand of its embodiments which have been more particularly envisaged; onthe contrary, it encompasses all variants thereof.

What is claimed is:
 1. A thermoplastic preform, having a body providedwith an at least partially longitudinally extended internal partitionand intended for the manufacture, by molding, of a container whose bodyhas opposed portions forming hollow recesses with inwardly-directedconcave surfaces, said recesses being braced by said internal partition,wherein the body of the preform has, in cross section, an outline ofnoncircular shape with two opposed portions (a, b) separated from eachother by a minimum distance (d₁) less than the distances separating theother pairwise opposed portions of said outline, wherein the internalpartition extends between said two opposed portions (a, b) separated bya minimum distance (d₁), and wherein said minimum distance (d₁) ischosen, with respect to the perimeter of the body of the preform, sothat, during molding, the internal partition undergoes a transversestretch ratio which has approximately the same value as the transverseor perimetric stretch ratio undergone by the body.
 2. Preform accordingto claim 1, wherein the body has a maximum transverse dimension (d₃),regarded as being parallel to the internal partition, which isappreciably less than the maximum transverse dimension (d₂), regarded asbeing approximately perpendicular to the internal partition, the ratioof said transverse dimensions (d₃, d₂) being such that, during molding,the internal partition undergoes a transverse stretch ratio which isapproximately identical to the transverse stretch ratio undergone by thebody.
 3. Preform according to claim 1, wherein the internal partitionextends centrally in a plane of symmetry of the body.
 4. Preformaccording to claim 1, wherein at least in its part in correspondencewith the internal partition, the body has a cylindrical contour. 5.Preform according to claim 3, wherein the cross section of the body isapproximately oval or elliptical, with the internal partition extendingapproximately along the minor axis of the oval or of the ellipse. 6.Preform according to claim 1, wherein the body has a bilobate outline,the internal partition extending between the two lobes.
 7. Preformaccording to claim 1, wherein the internal partition extends over theentire length of the body.
 8. Preform according to claim 1, wherein theinternal partition extends only over part of the length of the body, andin its part not provided with an internal partition, the body is acylinder of revolution.
 9. Preform according to claim 1, wherein saidmolding is blow molding.
 10. Preform according to claim 1, wherein saidmolding is stretch-blow molding.